The invention relates in general to an improvement in a wheel structure for vehicles. More specifically, the invention relates to reducing noise caused by a wheel structure.
FIG. 10 is a schematic diagram of a wheel which has heretofore been used, and which will be described with reference to FIG. 10. It has heretofore been known that columnar resonance occurring in a closed space defined by a tire 1 and a wheel 10 causes the deterioration of a load noise during vehicle travel. To be more exact, the columnar resonance is a resonance sound occurring when random vibration inputted from a road surface into the tire vibrates the air in the closed space 5 to cause a resonance phenomenon to occur in the vicinity of a columnar resonance frequency of the closed space 5.
This columnar frequency is generally determined on the basis of an equation:
fxe2x88x92c/2xcfx80r
wherein (f) is a columnar resonance frequency, (c) a sound velocity, and (r) a distance between the center of a wheel and a radially intermediate portion 20 of the closed space but peaks of the columnar resonance frequency occur plurally in practice due to the deformation, which is ascribed to the weight of the vehicle, of a ground contacting surface of the tire. In any case, a cross-sectional shape of the closed space 5 is constant at all times irrespective of the rotation of the wheel 12. Therefore, in a related art wheel structure, a value of the (r) of the above equation becomes constant. Accordingly, columnar resonance occurs with the same columnar resonance frequency at all times, and the resonance sound becomes offensive to the ear.
As a method of eliminating noise from a wheel, Japanese Patent Laid-Open No. 11704/1997 discloses techniques for reducing a noise of a wheel by providing a substantially cylindrical ring including a layer formed of at least one viscoelastic material on an outer circumferential surface of the wheel to thereby absorb mechanical vibration of the wheel. However, these techniques do not fundamentally hold down the occurrence of a columnar resonance sound, so that a satisfactory noise reducing effect cannot be obtained.
The invention has been made in view of the above-mentioned circumstances, and provides a wheel structure for vehicles, capable of effectively reducing a noise occurring due to a columnar resonance sound in a closed space in a wheel.
According to an aspect of the invention, the wheel structure has a wheel, and a tire fitted on an outer circumference of the wheel, a cross-sectional shape of a closed space defined by the wheel and tire being varied in a circumferential direction thereof so that a columnar resonance frequency of the closed space varies with a rotation of the wheel.
According to another aspect of the invention, projections are provided in parts of an inner side of the closed space, whereby a cross-sectional shape of the closed space varies in the circumferential direction thereof.
According to still another aspect of the invention, the projections are provided on an outer circumferential surface of a rim portion of the wheel.
According to a further aspect of the invention, the projections are provided on an inner circumferential surface of a tread of the tire.
According to another aspect of the invention, the projections are provided on inner circumferential surfaces of side walls of the tire.
According to still another aspect of the invention, a length of each of the projections 15 is substantially xc2xc of a circumferential length of the tire, two projections being provided in a circumferentially equally spaced manner.
According to a further aspect of the invention, a ratio of a cross-sectional area of each of the projections to that of the closed space which is not provided with the projection is set substantially not smaller than 2.5%.
According to another aspect of the invention, a circumferentially irregularly surfaced belt is fitted on an outer circumferential surface of the rim portion of the wheel to thereby circumferentially vary a cross-sectional shape of the closed space.
According to still another aspect of the invention, the outer circumferential surface of the rim portion of the wheel is formed irregularly in the circumferential direction to thereby circumferentially vary a cross-sectional shape of the closed space.
According to a further aspect of the invention, the closed space is formed so that a ratio of a length of a radially longest portion thereof to that of a radially shortest portion thereof becomes substantially not larger than 97%.